There's no doubt about it: We live in a plastic world. We wake up in the morning and brush our teeth with a plastic toothbrush and toothpaste squeezed from a plastic tube. We pour ourselves cereal from a plastic bag and milk from a plastic carton, work all day on a computer monitor and keyboard made of plastic, and return home for ­a nice dinner of chicken noodle soup from a can lined with, you guessed it: plastic. We might as well be Ken and Barbie.

Until recently, the abundance of plastic wasn't a pressing health concern, despite being on our environmental radar. Now a growing body of research links the chemical bisphenol-a (BPA), commonly found in a variety of consumer products, to a range of human health problems, including a higher risk of certain cancers, reduced fertility, birth defects and diabetes [source: Neimark, Zandonella].

BPA is the main component of polycarbonate, the hard, clear plastic sometimes used to make water bottles, baby bottles, food storage containers and other items like contact lenses, CDs and electronics devices. BPA is even used in places you wouldn't normally think of, like the protective lining in tin cans and in dental sealants. If you've noticed the little arrows stamped on plastic items with numbers inside, the number to look for here is 7. Although not all plastics labeled "7" contain BPA, it's still a good identifier, as are the letters "PC."

As of 2005, 94 of 115 peer-reviewed studies confirmed BPA's toxicity [source: Page]. For example, one study found that women with frequent miscarriages have approximately three times the blood levels of BPA as women with successful pregnancies [source: Bryson]. Yet the U.S. Food and Drug Administration maintains that the use of BPA in food-containing products is safe, and a U.S. National Institutes of Health panel declared BPA posed "negligible concern" concerning reproductive effects in adults [source: Neimark, Zandonella].

Despite the disagreement over BPA's actual impact on humans, several high-profile companies like Wal-Mart and Toys R Us have gone ahead and promised to phase out polycarbonate baby bottles and feeding products by the end of 2008. In addition, both Playtex (a major baby bottle manufacturer) and Nalgene (of water bottle fame) have pledged to stop using BPA in their products [source: Green Guide].

So is your kitchen full of BPA plastic a health hazard? Or is this publicity all just hype? Take a closer look into the BPA brouhaha on the next page.

Bisphenol-a Background

BPA disrupts the normal fetal development of mice; does that mean we can expect the same effects in humans?

If it weren't for a laboratory mishap roughly 10 years ago, it's possible you wouldn't be reading this article. But in August 1998, the geneticist Dr. Patricia Hunt was studying the ovaries of mice and noticed her data behaving strangely. For some reason, chromosomal errors leaped from 2 percent to 40 percent in the mice making up her control group. These abnormalities eventually would lead to miscarriage and birth defects. The determined cause: BPA [source: Neimark].

After running more tests, Hunt learned that all of the mice cages and water bottles were contaminated with BPA that had leached out of the polycarbonate plastic. When she replaced the plastics, the mice cells returned to normal. Her work revealed that exposure to BPA disrupts fetal development, as well as the eggs of the fetus that will be responsible for the next generation.

Since her discovery, Hunt and other researchers have become convinced that BPA is a cause for concern in humans, as well as mice. Critics of the studies linking BPA to cell damage, however, argue that the research isn't conclusive. Some point to a 2002 study showing that humans process BPA differently than mice, so we won't necessarily experience the same health effects. Others say that the BPA that finds its way into the food supply is safely below the limits set by the U.S. Environmental Protection Agency.

A plastics industry Web site called Bisphenol-A.org says BPA is completely safe unless you regularly eat 1,300 pounds (590 kilograms) of canned or bottled food a day [source: Zandonella]. The American Chemistry Council and the U.S. Food and Drug Administration seem to agree. Although the agency is reviewing its stance, it continues to downplay concerns about using products made with BPA [source: Dunham].

Other government bodies, such as the U.S. Department of Health and Human Services and the U.S. Centers for Disease Control and Prevention say that there is some concern about risks to humans who consume BPA. The differences of opinion among these factions arise partly because the ill effects of BPA are linked primarily with mice and partly because of the nature of the chemical itself.

BPA is a difficult substance to nail down; it doesn't behave like a typical toxin. While other chemicals labeled as toxic have clear-cut impacts (asbestos exposure leads to cancer, lead poisoning causes reduced mental capacity), BPA is sneakier. Rather than harm the body outright, BPA is an endocrine disruptor. It changes the way our body's hormones function, mimicking our own natural hormones -- in this case, estrogen.

Estrogen can alter the behavior of more than 200 genes, which control the growth and repair of nearly every organ and tissue in the body [source: Environmental Working Group]. Among other things, estrogen affects fetal development, cell structure and the onset of puberty, and your body's cells are highly sensitive to even tiny changes in estrogen levels.

Studies show that doses of BPA between 2 and 20 micrograms per kilogram of body weight alter the reproductive system of male mice. Babies fed canned formula heated in a polycarbonate bottle may consume that amount in just one day [source: Neimark]. So while some early toxicity studies done on BPA determined that high doses were safe, it's important to remember that BPA doesn't behave like your average toxin. Scientists aren't sure why, but high amounts of BPA don't always seem to affect genes the same way low doses do. It sounds counterintuitive, but with BPA, it turns out that less is actually more [source: Zandonella].

Should you, the consumer, swear off all plastics? Probably not. Learn some more sensible recommendations next.

BPA-free Bottles and Other Ways to Reduce BPA Exposure

Due to consumer demand, there are now many BPA-free options on the market

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Depending on who you listen to, BPA may or may not be a cause for concern, but there's no doubt that you're exposed. A 2004 study by the U.S. Centers for Disease Control and Prevention detected BPA in almost 93 percent of Americans [source: CDC]. A separate study by the Environmental Working Group, a U.S. nonprofit, found BPA in more than 50 percent of 97 commonly consumed canned goods at levels that caused adverse health effects in animal experiments [source: Environmental Working Group].

Mice seem to be harmed when they're exposed to BPA in those kinds of amounts, but does that mean people are too? Conclusive findings could take decades because the effects of estrogens may not show up until later in an individual's life. Thorough studies must follow a line of cells for many decades, and many people aren't willing to wait. Canada, for one, became the first country to officially declare BPA a toxic chemical, a decision that could lead to a partial or complete ban of its food-related use within two years. The European Union is also taking a more proactive approach, requiring companies to prove that a chemical is safe before it's cleared for the market. The U.S., on the other hand, requires proof that a chemical is not safe.

For countries where the government is taking a "wait and see" approach, never underestimate the power of you, the consumer. It was consumer demand that forced companies like Nalgene and Playtex to alter their products. Until other companies follow suit or the FDA changes its stance, there are several steps you can take to limit your exposure. And yes, one of those steps is to replace your beat-up polycarbonate water bottle and to stop using polycarbonate containers to hold food and beverages. If you'd rather not buy new containers, at least make sure yours aren't scratched and that you wash them by hand -- extreme heat and degradation increase the likelihood of BPA leaching out.